The present invention relates to a audio decoding device which is employed in a radio communication system such as a digital audio communication, a audio packet transmission, etc.
Then, a radio communication system to which the audio decoding device in the prior art is applied and which is employed in a normal digital audio communication, etc. will be explained hereunder. FIG. 10 is a block diagram showing a schematic configuration of a normal radio communication system.
As shown in FIG. 10, a radio communication system 1A comprises a plurality of mobile radio stations 2A and base radio stations 3A which relay and connect mutually these mobile radio stations 2A. A audio coding device which codes the input audio and then outputs a transmission signal and a audio decoding device which decodes an incoming received signal and then outputs the audio are built in each of these mobile radio stations 2A and base radio stations 3A.
FIG. 11 is a block diagram showing a schematic configuration of an interior of the audio coding device which corresponds to the audio decoding device in the prior art.
The audio coding device 8 shown in FIG. 11 comprises a audio input processing means 81 for digitally converting the input audio and then outputting the digital signal as audio data; a audio code processing means 82 for coding the audio data which are output from the audio input processing means 81 and then outputting the audio code; a transmission line code processing means 83 for calculating coded data to which redundancy is added to enable the conversion to the audio code once again even if an error is added to the audio code on the transmission line to some extent; a modulation processing means 84 for applying a modulation process to the coded data to output the transmission signal; and a transmission processing means 85 for transmitting the transmission signal which is modulated by the modulation processing means 84 onto the transmission line.
Then, the audio decoding device which has a function for receiving the transmission signal from the transmission processing means 85 in the audio coding device 8 via the transmission line and then decoding the received signal to output the audio will be explained hereunder.
In the prior art, as such audio decoding device, for example, a device set forth in Patent Application Publication (KOKAI) Hei 4-100422 has been known. FIG. 12 is a block diagram showing a schematic configuration of an interior of the audio decoding device in the prior art.
The audio decoding device 100 shown in FIG. 12 comprises a demodulation processing means 101 for receiving the signal, to which the error may be added over the transmission line, as the received signal and then demodulating the received signal into the coded data; an error correction processing means 102 for deciding whether or not the error is added to the coded data, then deciding whether or not the error is correctable if the error is added, then applying an error correction process to the coded data if the error is not added or if the added error is correctable, and then decoding the audio code to generate audio data; a audio decoding means 103 for decoding the audio code to generate the audio data; and a audio output processing means 104 for outputting the audio data which are output from the audio decoding means 103.
The error correction processing means 102 decodes the coded data to generate the audio code if the error is not added to the coded data, then applies the error correction process to the coded data if the error is not added to the coded data and the error is correctable, then decodes the coded data to generate the audio code, and then transmits the generated audio code to the audio decoding means 103 via a switch 105 and stores/holds the generated audio code and the coded data in a buffer 106 frame by frame.
Also, the error correction processing means 102 generates interpolation process information based on the coded data if the error is added to the coded data and the error is uncorrectable, then reads the audio code, which corresponds to the coded data being equivalent to the preceding frame of the coded data, from the buffer 106 without decoding the coded data, and then transmits the read audio code to the audio decoding means 103 via the switch 105 based on the interpolation process information.
In this manner, according to the audio decoding device in the prior art, even in the case that the uncorrectable error is added to the coded data, the interpolation process of the coded data containing the uncorrectable error can be achieved by reading the audio code, which is concerned with the coded data being equivalent to the preceding frame of the coded data containing the uncorrectable error, from the buffer 106 and then transmitting the audio code to the audio decoding means 103.
However, according to the above audio-decoding device in the prior art, in the case that the audio data is generated by decoding the audio code, which is concerned with the coded data containing the uncorrectable error caused due to, for example, aggravating circumstances of the transmission line, as shown in FIG. 13, the audio code which associates with the preceding frame is read from the buffer 106 in unit of frame based on the interpolation process information, in place of decoding of the audio data containing the uncorrectable error (step S101), then the audio code is transmitted to the audio decoding means 103 (step S102), then the interpolation process is executed in unit of frame (step S103), and then the audio code is decoded to generate the audio data (step S104). Therefore, there is a problem that distortion or disconnection of the output audio is generated by carrying out the interpolation process in unit of frame.
The present invention has been made in light of the above problems, and it is an object of the present invention to provide a audio decoding device which is capable of suppressing generation of the distortion and the disconnection of the output audio to the minimum even when the signal which contains the uncorrectable error caused due to the aggravating circumstances of the transmission line is received.
In order to achieve the above object, a audio decoding device of the present invention comprises a reception processing means for receiving a signal from a transmission line as a received signal; a demodulation processing means for demodulating the received signal which is received by the reception processing means into coded data; a soft decision information generating means for generating a soft decision information indicating a current situation of the transmission line, based on coded data which are demodulated by the demodulation processing means; an error correction processing means for decoding the coded data to output a audio code and also outputting interpolation process information based on the coded data if it is decided that an uncorrectable error is added to the coded data which are demodulated by the demodulation processing means; a audio decoding processing means for reading interpolation information in a preceding frame based on interpolation process information concerning to the audio code, then applying an interpolation process to the audio code in unit of bit based on interpolation information and soft decision information, and then generating audio data by decoding the audio code which is subjected to the interpolation process if the audio code associated with the coded data, to which the uncorrectable error is added, is received from the error correction processing means; and a audio output processing means for outputting the audio data generated by the audio decoding processing means.
Therefore, according to the audio decoding device of the present invention, if the uncorrectable error is caused due to the aggravating circumstances of the transmission line, the interpolation process can be applied to the audio code in unit of bit by using the soft decision information indicating the current situation of the transmission line as well as the interpolation information in decoding, in place of application of the interpolation process to the audio code in unit of frame by using only the interpolation information in the prior art. As a result, while maintaining continuity of a audio waveform in the audio data after the decoding has been completed, generation of distortion and disconnection of the audio can be suppressed to the minimum by providing the optimum interpolation process which can mate with the current situation of the transmission line.
A audio decoding device of the first aspect of the present invention comprises a reception processing means for receiving a signal from a transmission line as a received signal; a demodulation processing means for demodulating the received signal which is received by the reception processing means into coded data; a soft decision information generating means for generating a soft decision information indicating a current situation of the transmission line, based on coded data which are demodulated by the demodulation processing means; an error correction processing means for decoding the coded data to output a audio code and also outputting interpolation process information based on the coded data if it is decided that an uncorrectable error is added to the coded data which are demodulated by the demodulation processing means; a audio decoding processing means for reading interpolation information in a preceding frame based on interpolation process information concerning to the audio code, then applying an interpolation process to the audio code in unit of bit based on interpolation information and soft decision information, and then generating audio data by decoding the audio code which is subjected to the interpolation process if the audio code associated with the coded data, to which the uncorrectable error is added, is received from the error correction processing means; and a audio output processing means for outputting the audio data generated by the audio decoding processing means.
Therefore, according to the audio decoding device of the first aspect of the present invention, there is provided the soft decision information generating means which generates the soft decision information indicating the current situation of the transmission line based on the coded data being demodulated by the demodulation processing means. Even if the audio code which is concerned with the coded data containing the uncorrectable error caused due to the aggravating circumstances of the transmission line is received from the error correction processing means, the interpolation information in the preceding frame can be read based on the interpolation process information concerning to the audio code, then the interpolation process can be applied to the audio code in unit of bit based on the interpolation information and the soft decision information, and then the audio code which is subjected to the interpolation process can be decoded to generate the audio data. As a result, while maintaining continuity of a audio waveform in the audio data after the decoding has been completed, generation of distortion and disconnection of the audio can be suppressed to the minimum by providing the optimum interpolation process which can mate with the current situation of the transmission line.
Preferably, in a audio decoding device as mentioned above, the error correction processing means may stores and holds the audio code and the coded data frame by frame as the interpolation information when the coded data which are demodulated by the demodulation processing means and to which no error is added is decoded to output the audio code, or when an error correction process is applied to the coded data which are demodulated by the demodulation processing means and to which the correctable error is added and then the coded data which are subjected to the error correction process are decoded to output the audio code.
Therefore, according to the audio decoding device, the audio code and the coded data which are generated by decoding the coded data to which no error is added or the coded data to which the correctable error is added are stored and held in unit of frame as the interpolation information. Therefore, continuity of the audio can be assured by applying the optimum interpolation process to the audio code, to which the uncorrectable error is added, based on the interpolation information concerning to the preceding frame.
Preferably, in a audio decoding device, the soft decision information generating means may includes data extracting means for extracting a receiving electric field strength from the coded data which are demodulated by the demodulation processing means, and also extracting phase information of symbol points from the coded data, and soft decision information calculation processing means for generating soft decision information indicating the current situation of the transmission line, based on the receiving electric field strength and the phase information which are extracted by the data extracting means.
Therefore, according to the audio decoding, the receiving electric field strength and the phase information at the symbol points can be extracted from the coded data and then the soft decision information indicating the current situation of the transmission line can be generated based on the receiving electric field strength and the phase information. Therefore, the soft decision information generating means can cope sufficiently with the signal error which is generated due to the aggravating circumstances of the transmission line.
A audio decoding device according to the second aspect of the present invention is characterized by comprising a reception processing means for receiving a signal from a transmission line as a received signal; a demodulation processing means for demodulating the received signal which is received by the reception processing means into coded data; a soft decision information generating means for generating a soft decision information indicating a current situation of the transmission line, based on coded data which are demodulated by the demodulation processing means; an error correction processing means for decoding the coded data demodulated by the demodulation processing means to output a audio code and also outputting interpolation process information concerning to the coded data if it is decided that an uncorrectable error is added to the coded data; an error correction processing situation analyzing means for analyzing an error added situation of the audio code which is output from the error correction processing means; an optimization audio decoding processing means for selecting an optimum audio decoding means, based on an analyzed result obtained by the error correction processing situation analyzing means, out of a normal process type audio decoding means which decodes the audio code output from the error correction processing means to generate the audio data, an interpolation process type audio decoding means which applies the interpolation process to the audio code output from the error correction processing means in unit of bit based on the interpolation process information and the soft decision information and then decodes the audio code which is subjected to the interpolation process to generate the audio data, and an optimization process type audio decoding means which applies an optimizing process to the audio code output from the error correction processing means and then decodes the audio code which is subjected to the optimizing process to generate the audio data, and then outputting the audio data generated by a selected audio decoding means; and a audio output processing means for outputting the audio data generated by the audio decoding processing means.
Therefore, according to the audio decoding, there is provided the soft decision information generating means which generates the soft decision information indicating the current situation of the transmission line based on the coded data demodulated by the demodulation processing means. If the audio code which is concerned with the coded data containing the uncorrectable error caused due to the aggravating circumstances of the transmission line is received from the error correction processing means, the interpolation process can be applied to the audio code, which is output from the error correction processing means, in unit of bit based on the interpolation information and the soft decision information, and then the audio code which is subjected to the interpolation process can be decoded to generate the audio data. As a result, while maintaining continuity of a audio waveform in the audio data after the decoding has been completed, generation of distortion and disconnection of the audio can be suppressed to the minimum by providing the optimum interpolation process which can mate with the current situation of the transmission line.
Therefore, according to the audio decoding device of the second aspect of the present invention, the optimum audio decoding means out of the normal process type audio decoding means, the interpolation process type audio decoding means, and the optimization process type audio decoding means in the optimization audio decoding processing means can be selected based on the analyzed result obtained by the error correction processing situation analyzing means which analyzes the error added situation in the audio code which is output from the error correction processing means. As a result, the optimum audio decoding process which corresponds to the current error added situation can be provided.
Preferably, in a audio decoding device as described above, the soft decision information generating means may includes a data extracting means for extracting a receiving electric field strength from the coded data which are demodulated by the demodulation processing means, and also extracting phase information of symbol points from the coded data, and a soft decision information calculation processing means for generating soft decision information indicating the current situation of the transmission line, based on the receiving electric field strength and the phase information which are extracted by the data extracting means.
Therefore, according to the audio decoding device, the receiving electric field strength and the phase information at the symbol points can be extracted from the coded data and then the soft decision information indicating the current situation of the transmission line can be generated based on the receiving electric field strength and the phase information. Therefore, the soft decision information generating means 22a can cope sufficiently with the signal error which is generated due to the aggravating circumstances of the transmission line.
Preferably, in a audio decoding device, the error correction processing means may include an error correction demodulation processing means for applying the error correction process to the coded data which are demodulated by the demodulation processing means bit by bit based on the soft decision information which is generated by the soft decision information generating means, and then decoding the coded data which are subjected to the error correction process to output the audio code.
Therefore, according to the audio decoding device, the error correction process can be applied to the coded data, which are demodulated by the demodulation processing means, bit by bit based on the soft decision information prior to the process in the optimization audio decoding processing means. Therefore, the frequency of the interpolation process in the optimization audio decoding processing means can be reduced.
Preferably, in a audio decoding device, the error correction processing means may include an error check bit calculating means for checking whether or not the error is added to the audio code output from the error correction decoding processing means, and then outputting a checked result as an error check bit.
Therefore, according to the audio decoding device, it is possible to output the error check bit indicating the checked result to show whether or not the error is added to the audio code. Therefore, the processing efficiency in the succeeding error correction processing situation analyzing means which analyzes the error added situation can be improved.
In a audio decoding device, the error correction processing situation analyzing means includes a audio code error deciding means for deciding whether or not the error is added to the audio code which is output from the error correction processing means, based on the error check bit supplied from error check bit calculating means.
Therefore, it can be decided, based on the error check bit, whether or not the error is added to the audio code which is output from the error correction processing means.
Preferably, in a audio decoding device, the optimization audio decoding processing means may includes a audio decoding process storing means for storing sequentially contents of the audio decoding process, which are concerned with a selected audio decoding means, into a audio decoding process storage buffer every frame of the audio data when the audio data which are generated by the selected audio decoding means are output.
Therefore, according to the audio decoding device, the contents of the audio decoding process which is concerned with the selected audio decoding means every frame of the audio data are stored sequentially into the audio decoding process storage buffer when the audio data which is generated by the selected audio decoding means in the optimization audio decoding processing means are output. Therefore, the audio decoding process storing means can recognize by which audio decoding means the audio decoding process is applied frame by frame, and also can use effectively the contents of the audio decoding process in every frame in the succeeding interpolation process.
Preferably, in a audio decoding, the error correction processing situation analyzing means includes an error correctability deciding means for deciding whether or not the error which is added to the audio code is correctable, based on contents of the audio decoding process associated with the audio decoding means which is selected by a preceding frame stored in a audio decoding process storage buffer, if it is decided by the audio code error deciding means that the error is added to the audio code.
Therefore, according to the audio decoding device, it can be decided whether or not the error which is added to the audio code is correctable, based on the contents of the audio decoding process which is concerned with the optimum audio decoding means selected by the preceding frame stored in the audio decoding processing storage buffer.
Preferably, in a audio decoding device, the optimization audio decoding processing means selects the normal process type audio decoding means if it is decided by the audio code error deciding means that no error is added to the audio code, and the selected normal process type audio decoding means decodes the audio code which is output from the error correction processing means to generate the audio data.
Therefore, according to the audio decoding device, if it decided by the audio code error deciding means that the error is not added to the audio code, the audio code error deciding means selects the normal process type audio decoding means to execute the normal audio decoding process. Therefore, the optimum audio decoding process to correspond to the current error added situation can be provided.
Preferably, in a audio decoding device, the optimization audio decoding processing means includes a audio information storage means for storing sequentially the audio data and the audio code into a audio information storage buffer every frame when the audio data which are generated by the selected audio decoding means are output.
Therefore, according to the audio decoding device, the audio data and the audio code are stored sequentially into the audio information storage buffer every frame when the audio data generated by the selected audio decoding means are output. Therefore, the audio information storing means can recognize the audio data and the audio code frame by frame and also can use effectively the audio data and the audio code in every frame in the succeeding interpolation process.
Preferably, in a audio decoding device, the optimization audio decoding processing means selects the interpolation process type audio decoding means if it is decided by an error correctability deciding means that the error which is added to the audio code is uncorrectable, and the selected interpolation process type audio decoding means reads the audio data and the audio code, which are stored in the audio information storage buffer and are concerned with the preceding frame, as the interpolation information based on the interpolation process information concerning to the audio code, then applies the interpolation process to the audio code to which the uncorrectable error is added in unit of bit based on the interpolation information and the soft decision information, and then decodes the audio code which is subjected to the interpolation process to generate the audio data, if the audio code which is output from the error correction processing means and to which the uncorrectable error is added is received.
Therefore, according to the audio decoding, the error correctability deciding means can select the interpolation process type audio decoding means to execute the audio decoding process together with the interpolation process if it decides that the error being added to the audio code is uncorrectable. Therefore, the optimum audio decoding process to correspond to the current error added situation can be provided.
Preferably, in a audio decoding device, the optimization audio decoding processing means selects the optimization process type audio decoding means if it is decided by the error correctability deciding means that the error which is added to the audio code is correctable, and the selected optimization process type audio decoding means applies an optimizing process to the audio code which is output from the error correction processing means, and then decodes the audio code which is subjected to the optimizing process to generate the audio data.
Therefore, according to the audio decoding device, the error correctability deciding means can select the optimization process type audio decoding means to execute the audio decoding process together with the optimization process if it decides that the error being added to the audio code is correctable. Therefore, the optimum audio decoding process to correspond to the current error added situation can be provided.
Preferably, in a audio decoding device, the optimization process type audio decoding means includes an optimizing normal process type audio decoding means for decoding the audio code to generate the audio data if it is decided by the error correctability deciding means that the error which is added to the audio code is correctable.
Therefore, according to the audio decoding device, if it is decided by the error correctability deciding means that the error which is added to the audio code is correctable, the audio data can be generated by decoding the audio code.
Preferably, in a audio decoding device, the optimization process type audio decoding means may includes a audio decision processing means for calculating a correlation value between the audio data generated by the optimizing normal process type audio decoding means and the audio data in the preceding frame stored in the audio information storage buffer, then deciding whether or not a calculated correlation value is in excess of a threshold value, and the optimization process type audio decoding means sets the audio data generated by the optimizing normal process type audio decoding means as the audio data generated in the optimization process type audio decoding means if it is decided by the audio decision processing means that the calculated correlation value exceeds the threshold value.
Therefore, according to the audio decoding device, if it is decided by the audio decision processing means that the correlation value is in excess of the threshold value, the audio decision processing means decides the audio data as the audio, and then sets the audio data generated by the optimizing normal process type audio decoding means as the audio data generated in the optimization process type audio decoding means.
Preferably, in a audio decoding device, the optimization process type audio decoding means includes an interpolation process deciding means for counting sequentially a number of times of the audio decoding process frame by frame by using the optimizing normal process type audio decoding means, and then deciding whether or not the number of times of the audio decoding process exceeds a predetermined number of times if it is decided by the audio decision processing means that the correlation value is not in excess of the threshold value, and an optimizing interpolation process type audio decoding means for applying the interpolation process to the audio code being output from the error correction processing means bit by bit based on the soft decision information and the audio code concerning to the preceding frame which is stored in the audio information storage buffer, then decoding the audio code which is subjected to the interpolation process to generate the audio data, and then setting such audio data as the audio data generated in the optimization process type audio decoding means if it is decided by the interpolation process deciding means that the number of times of the audio decoding process in every frame exceeds the predetermined number of times.
Therefore, according to the audio decoding device, if it is decided by the audio decision processing means that the correlation value does not exceed the threshold value, the interpolation process deciding means decides that the audio data is not the audio, then decides that the number of times of the audio decoding process exceeds the predetermined number of times, and then shifts the process to the audio decoding process in the optimizing interpolation process type audio decoding means if it is decided that the number of times of the audio decoding process exceeds the predetermined number of times. Therefore, prior to the audio decoding process in the optimizing interpolation process type audio decoding means, the audio codes can be estimated as much as possible and also the interpolation process executed by the optimizing interpolation process type audio decoding means is applied only to the audio codes which cannot be estimated, so that the frequency of the interpolation process can be reduced as small as possible and thus generation of the distortion and disconnection of the audio can be suppressed to the minimum while maintaining continuity of the audio waveform.
Preferably, in a audio decoding device, the optimization process type audio decoding means includes a audio code optimization processing means for detecting likelihood of respective elements of the audio code which is output from the error correction processing means based on the soft decision information, then applying bit inversion to low likelihood elements of the audio code, and then generating the audio code which is subjected to the bit inversion, if it is decided by the interpolation process deciding means that the number of times of the audio decoding process in every frame does not exceed the predetermined number of times, and the optimizing normal process type audio decoding means decodes the audio code which is generated by the audio code optimization processing means and which is subjected to the bit inversion to generate the audio data.
Therefore, according to the audio decoding, if it is decided by the interpolation process deciding means that the number of times of the audio decoding process in every frame does not exceed the predetermined number of times, the audio code optimization processing means detects likelihood of respective elements of the audio code being output by the error correction processing means based on the soft decision information, then applies the bit inversion to the low likelihood elements of the audio code, and then decodes the audio code which is subjected to the bit inversion by the optimizing normal process type audio decoding means. Therefore, prior to the audio decoding process in the optimizing interpolation process type audio decoding means, the audio codes can be estimated as much as possible and also the interpolation process executed by the optimizing interpolation process type audio decoding means is applied only to the audio codes which cannot be estimated, so that the frequency of the interpolation process can be reduced as small as possible and thus generation of the distortion and disconnection of the audio can be suppressed to the minimum while maintaining continuity of the audio waveform.